In the bottling industry the known technology for filling containers such as bottles, cans and jars involves the use of filling machines equipped with a plurality of filler heads each of which is fitted with a filler valve.
In the known method there are electro-pneumatic filler valves fitted with an electronic control system operating pneumatic actuators which control the movements of the moving parts of the valves.
In the sector for filling plastic containers, such as those made of PET, with liquids which are sensitive to oxygen, the filling stage is preceded by a flushing stage where an inert gas or carbon dioxide is injected into the container in order to eliminate any oxygen present in the container.
Flushing is used with PET containers in particular because a vacuum method cannot be used: creating a high vacuum inside a container made from PET would irreparably damage the container.
The known types of filler valves have a first pipe for feeding out a liquid from a tank and a second pipe designed to allow the gas, previously injected into the container, to escape during the filling stage.
The second pipe is coaxially positioned inside the liquid feed pipe and slides up and down inside this pipe so that it can be inserted into the container. Usually the second pipe has a projection on its outer surface at a point between its two ends. This projection acts a stop valve inside the liquid feed pipe. When the second pipe moves up and down, the projection opens and closes the space where the liquid flows through.
In another version of the know method, there is no first liquid feed pipe and the tank containing the liquid to be filled is directly connected to the container to be filled by a passage which is alternately opened and closed by a mobile valve which is usually coaxial to the second pipe which in this case is fixed.
According to this known method, the filler valve is usually fixed and the container to be filled, a PET bottle for example, moves up and down with an alternating motion on the vertical axis. The container moves between two positions. In the first, flushing position, the container is moved close to the feed section of the valve so as to allow the second pipe to enter the container and inject the gas. In the flushing position, the mouth of the container is not resting sealed against the feed section of the valve. In the second filling position the container is moved towards the filler valve so that the mouth of the container rests against and is sealed to the feed section of the valve. This action prevents oxygen from entering the container during filling.
In addition to the two operating positions described above, the container also has a rest position which is the position it takes up when the filling machine is being loaded.
FIG. 1 shows the prior art where the container is usually moved by a pneumatic cylinder 100. In the case where PET bottles 101 are being filled, the pneumatic cylinder has pickup means 102 for holding the neck of the container. At present, the duration of the flushing stage is controlled by a suitably shaped mechanical cam 103 and a roller 104 running on the cam and connected to the pneumatic cylinder 100.
On rotary filling machines this cam has a two-step profile with:                a first section at a fixed height from the floor;        a downward connecting section followed by a second section at a fixed height which is lower than that of the first section;        an upward section followed by a third section at a fixed height which is substantially the same as the height of the first section.        
The fixed height sections and the connecting sections alternate in the direction of rotation of the filling machine.
The length of the second (lower) fixed height section is used to define the duration of the flushing stage.
The roller connected to the pneumatic cylinder follows the cam profile so that the container first moves downwards from the loading position to the flushing to position and then moves upwards from the flushing position to the filling position.
In brief, filler valves of the known type require a cam with a predefined profile and length in order to control movements of the container and to control its distance from the filler valve; the cam profile and length control the duration of the filler stage.
The filler valves briefly described above have considerable disadvantages.
The main disadvantage is that they do not permit size changeovers. In cases where containers of a different size are to be filled, the filling machine must be stopped and the cam must be substituted with another cam which has a suitable length and profile for the new flushing stage duration. The duration of the flushing stage is substantially proportional to the volume of the container to be filled. As the volume of the container increases so too does the time needed to completely flush out the oxygen inside the container.
A further disadvantage of fillers valves of the known type is that in the event of a machine stoppage they do not permit the completion of the filling cycle for containers which have already been flushed but which have not yet reached the feed section of the valve. The presence of a cam with a predefined and fixed profile does not allow the container to approach the feed section of the valve in order to start filling and expel the flushing fluid. This allows oxygen to enter the container once again. This causes unnecessary waste of carbon dioxide or inert gas. This also causes a loss of productivity because the containers which have been treated with gas but not filled must be thrown away.